Believe it or not I've got vaseline in the diff with mobil synthetic grease on the ring and pinion. I thought that I'd try it and see what happened since others over at savage-central are using it with good results. I'm probably going to pack the front with the mobil and compare them when I break it back down for a checkup. Considering how much stress those bearings see I'd not go to the trouble of doing the cups then skimp on the bearings only to have them fail later. When I did it the first time I couldn't get any bearings so I was forced to reuse the ones I had and the one on the ring side failed quickly. If you're using the plastic diff cups you'll want to use machine screws to secure the ring gear to the cup as they don't back out like the self threading type does.